1. Field of the Invention
This invention relates to arc-tangent circuits. More specifically, the invention is an arc-tangent circuit capable of providing a continuous and linear output over 360.degree..
2. Description of the Related Art
One of the most useful trigonometric functions is the arc-tangent. The arc-tangent is used to determine an angle .theta. where either the sine and cosine values of the angle are known or where the angle is part of a right triangle in which the magnitudes of adjacent and opposite sides of the triangle (relative to the angle) are known. Specifically, as is well known, the angle .theta. is equal to either EQU .theta.=arc-tangent (sin(.theta.)/cos(.theta.))
or EQU .theta.=arc-tangent(opposite side/adjacent side)
The arc-tangent function is useful in resolver devices where device output is provided in terms of sine and cosine values of a resolver shaft angle over a shaft rotation of 360.degree.. Thus, the shaft angle can be determined by applying the arc-tangent function to the resolver outputs. However, the arc-tangent function introduces two inherent problems into the determination of resolver shaft angle. First, the arc-tangent function repeats itself every 180.degree.. Second, when the cosine value approaches zero, the arc-tangent approaches infinity.